Food Chemistry and Major Constituents

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Questions and Answers

Which type of food is classified as Energy Yielding Foods (EYF)?

Foods rich in proteins, such as milk and meat

Foods containing high biological value proteins

Foods rich in carbohydrates and fats (correct)

Foods rich in vitamins and minerals

What is the primary role of Body Building Foods (BBF)?

Provide essential vitamins for the immune system

Supply energy for physical activity

Support the synthesis of body tissues (correct)

Act as a dispersing medium in food

What does water activity (aw) specifically refer to?

The energy provided by water in food

The amount of water absorbed by food

The total moisture content in food

The form in which water exists in food (correct)

Which of the following is NOT classified as a major constituent of food?

Vitamins Signup and view all the answers

Which foods fall under the category of Protective Foods (PF)?

Vegetables and fruits Signup and view all the answers

What is the primary energy contribution of 1 gm of fat?

9 K-calories Signup and view all the answers

Which form of water is primarily responsible for moisture content in food?

Free water Signup and view all the answers

Which of the following is an example of food high in proteins of high biological value?

Milk and eggs Signup and view all the answers

What best describes free water in food?

Water that acts as a dispersing agent and solvent Signup and view all the answers

How does bound water in food affect microbial activity?

It is practically unavailable for microbiological activities Signup and view all the answers

What is the water activity (aw) of pure distilled water?

1.0 Signup and view all the answers

Which factor directly affects the shelf life of food?

The water activity (aw) Signup and view all the answers

How is water activity (aw) calculated?

As a ratio of the vapor pressures of a substance and pure water Signup and view all the answers

Which organisms cannot grow below a water activity (aw) of 0.8?

Bacteria Signup and view all the answers

What happens to water activity (aw) as the percentage of bound water increases?

Water activity decreases Signup and view all the answers

What role do humectants play in food science?

They bind water, reducing water activity Signup and view all the answers

What does water activity (aw) measure?

The availability of water for biological reactions Signup and view all the answers

How is relative humidity (RH) calculated from water activity (aw)?

RH = (aw) × 100 Signup and view all the answers

Which microorganism generally requires a water activity value of at least 0.91 to grow?

Bacteria Signup and view all the answers

What is the term for the relative humidity at which a food product maintains its natural moisture without gaining or losing water?

Equilibrium relative humidity (ERH) Signup and view all the answers

Which of the following substances falls within the water activity range of 0.87 to 0.80?

Syrups Signup and view all the answers

What directly influences the physical properties of a food substance such as weight and density?

Moisture content Signup and view all the answers

Which statement about water migration is true?

Water migrates from areas of high aw to areas of low aw. Signup and view all the answers

What type of microorganisms requires a water activity of at least 0.6 to grow?

Fungi Signup and view all the answers

What is the primary reason for measuring water activity in food?

To inhibit mold growth and extend shelf-life. Signup and view all the answers

At what water activity level can pathogenic microorganisms generally not grow?

0.86 Signup and view all the answers

How does decreased water activity affect food preservation?

Slows enzyme reactions and inhibits microbial growth. Signup and view all the answers

Which types of microorganisms can thrive at water activity values between 0.6 and 0.65?

Mold and osmophilic yeast. Signup and view all the answers

What is the oldest method of food preservation mentioned?

Dehydration. Signup and view all the answers

What critical point in food safety can water activity be used for?

Establishing control points in HACCP programs. Signup and view all the answers

What potential problem can occur if a hermetically sealed package experiences condensation?

Microbial contamination can increase. Signup and view all the answers

Why are dry foods considered more stable than wet foods?

Any remaining water has low activity. Signup and view all the answers

Study Notes

Food Chemistry

Food chemistry studies chemical processes and interactions within food.
It analyzes the composition, structure, and properties of foods.
Examines chemical changes during processing and consumption.
Addresses the chemistry of water, carbohydrates, proteins, lipids, vitamins, minerals, and enzymes.

Major Food Constituents

Food contains major constituents: carbohydrates, fats, and proteins.
Minor constituents: vitamins, minerals, enzymes, pigments, flavors, acids, and water.

Food Classification by Function

Energy Yielding Foods (EYF): Rich in carbohydrates and fats.
- 1 gram of carbohydrate provides 4 kilocalories.
- 1 gram of fat provides 9 kilocalories.
Body Building Foods (BBF): Rich in proteins.
- Milk, meat, eggs, and fish are good sources of high biological value proteins.
Protective Foods (PF): Rich in vitamins, minerals, and proteins.
- Two categories:
  - Foods high in vitamins, minerals, and proteins (milk, eggs, fish, liver).
  - Foods rich in vitamins and minerals (green leafy vegetables and some fruits).

Water in Food

Water is an essential food component.
It exists as an intracellular or extracellular component in plant and animal products.
Water acts as a dispersing medium and solvent.
The presence of water in food:
- Moisture content: Amount of water present.
- Water activity (aw): The form in which water exists.

Forms of Water in Food

Free water: Most abundant form, easily removed by drying.
- Acts as a dispersing agent and solvent.
Absorbed water: Attached to the surface of molecules like polysaccharides and proteins.
- Not easily squeezed out.
Bound water: Tightly bound to macromolecules or organelles.
- Unavailable for microbial activity or quality degradation.
- Freezes at very low temperatures.

Water Activity (aw)

Water activity is the measure of available water for microbial, enzymatic, or chemical reactions.
It represents the amount of free water in a sample.
Influences the shelf life of food.
Each microorganism has a critical aw below which it cannot grow.

Water Activity and Food Preservation

Lowering aw retards microbial growth, enzyme activity, and non-enzymatic browning.
Additives with high water binding capacity (humectants) are used to decrease aw, including common salts, glycerol, and sucrose.

Calculating Water Activity

aw is the ratio of water vapor pressure of a substance to the vapor pressure of pure water at the same temperature.
aw = P / P0
- P: vapor pressure of water in the substance.
- P0: vapor pressure of pure water.
Bound water is inversely related to water activity.
Pure distilled water has an aw of 1.0.
Temperature influences vapor pressure.

Water Activity Meter (Manometer)

Used to measure aw.

Relative Humidity and Water Activity

Relative humidity (RH) is the percentage of water vapor in the air.
aw is a fraction, so RH = aw x 100.
Equilibrium relative humidity (ERH): RH at which the food neither gains nor loses moisture.

Microbial Growth and Water Activity

Microbial growth is directly linked to aw.
Water migrates from high aw to low aw areas.
Different microorganisms have different aw requirements for growth.
Higher aw typically supports more microorganisms.
Bacteria generally require aw ≥ 0.91, fungi ≥ 0.6.

Moisture Content vs. Water Activity

Moisture content: The amount of water in a product.
Water Activity: A measure of available water for microbial growth.

Water Activity and Food Shelf Life

Water activity is a critical factor in food product design and safety.
Maintaining a low aw can inhibit mold growth and extend shelf life.
Water activity is used as a critical control point in Hazard Analysis and Critical Control Points (HACCP) programs.

Dehydration and Food Preservation

Dehydration is a traditional method of food preservation.
Removing water reduces aw, making it unavailable for microbial growth.
Dry foods are more stable than wet foods due to low aw.
Drying prevents the growth of food poisoning bacteria.
Osmophilic yeasts and some molds can grow at aw between 0.6 to 0.65.

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Description

Explore the fascinating field of food chemistry, where chemical processes shape the composition and properties of food. This quiz covers the major and minor constituents of food, their functions, and the energy they provide. Test your understanding of how different food types contribute to health and nutrition.